Conventionally, a power element unit making an inverter control of an electric rotating machine has been generally located apart from the electric rotating machine. Therefore, an AC wiring for providing an electrical connection between the power element unit and the electric rotating machine becomes longer, and thus a voltage drop is increased due to wiring resistance, so that a problem exists in that torque and velocity of the electric rotating machine are decreased. In particular, in a vehicle electric rotating machine with a power supply at low voltage of 12V and 36V, the influence of this voltage drop is large. For example, on the supposition of voltage drop of 0.5V, there is a loss of approximately 4% power supply voltage. Moreover, although measures of making wires thicker can be conceived for suppressing voltage drop, a problem exists in that weight of routing wires is increased, and thus costs are increased.
Furthermore, even if it is not an electric rotating machine of a low voltage power supply, when any power element unit and any electric rotating machine are disposed spaced apart from each other, it is necessary to provide with a long wiring. Thus, not only the layout of products is restricted, but also cost of wiring parts or assembling cost is increased.
To overcome this, for example, as shown in Patent Document 1 (the Japanese Patent Publication (unexamined) No. 225000/2003), a technique in which a control device is integrally mounted onto a vehicle electric rotating machine is considered. Due to that the control device is mounted on a rear bracket as an integral part, it is certainly possible to shorten harnesses to use for connection, to suppress voltage drop to improve torque characteristics or revolution number characteristics of an electric rotating machine, and further to avoid the increase of weight or the increase of cost.
However, as shown in the Patent Document 1 (claim 5, paragraph number [0039], FIG. 4 or the like), to dispose a control device in the vicinity of an electric rotating machine, it is necessary to ensure heat dissipation of a power element. Nevertheless, since the electric rotating machine itself generates heat, temperature environments therearound become tough. Further, due to that a control circuit containing power elements, being heating elements, is located in the vicinity of the electric rotating machine, temperatures further rise, resulting in a problem of destruction of the power element or the control element. Moreover, since a power element unit is added and mounted in a space of the electric rotating machine, a further problem exists in that the whole device becomes larger.
FIG. 13 is a schematic circuit diagram for explaining operation of an electric rotating machine provided with a power element unit. In the diagram, an electric rotating machine 1 is provided with an armature winding 16a wound around a stator, and a field winding 14 wound around a rotor. The mentioned armature winding 16a is constructed of three phases (U-phase, V-phase, and W-phase) of coils in Y-connection (star-connection). A power element unit 4 is provided with an inverter module 40 that is formed of a plurality of switching elements, being power elements (power transistor, MOSFET, IGBT and the like) 41 and diodes 42 connected in parallel to each of the switching elements 41, and a capacitor 43 that is connected in parallel to this inverter module 40. In the inverter module 40, letting a pair of the switching element 41a and diode 42 forming an upper arm 46 and the switching element 41b and diode 42 forming a lower arm 47 that are connected in series one set, these three sets are connected in parallel.
The ends of each phase of Y-connection in the armature winding 16a are electrically connected to intermediate points between the mentioned switching elements 41a of the upper arm 46 and the switching elements 41b of the lower arm 47 that are located in series via an AC wiring 9. Furthermore, a positive electrode terminal and a negative electrode terminal of a battery 5 are electrically connected to the positive electrode side and negative electrode side of the inverter module 40 via a DC wiring 8 respectively. In the inverter module 40, the switching operation of each of the switching element 41a and 41b is controlled by commands from a control circuit 44. Further, the control circuit 44 controls a field current control circuit 45 to adjust a field current to flow through the field winding 14 of the rotor.
In the electric rotating machine 1 provided with the power element unit 4 as mentioned above, at the time of starting the engine, a DC power is supplied to the power element unit 4 via the DC wiring 8 from the battery 5. Then, the control circuit 44 makes ON/OFF control of each of the switching elements 41a and 41b of the inverter module 40, and a DC power is converted to a three-phase AC power. Subsequently, this three-phase AC power is supplied to the armature winding 16a of the electric rotating machine 1 via the AC wiring 9. Accordingly, a rotating magnetic field is formed around the field winding 14 of the rotor through which a field current is carried by means of the field current control circuit 45, the rotor is driven to rotate, and then the engine is started via a pulley for the electric rotating machine, a belt, a crank pulley, and a clutch (ON).
When an engine is started, a rotational power of the engine is transmitted to the electric rotating machine 1 via the crank pulley, belt, and pulley for the electric rotating machine. Accordingly, the rotor is driven to rotate resulting in induction of a three-phase AC voltage at the armature winding 16a. Then, the control circuit 44 makes ON/OFF control of each of the switching elements 41, the three-phase AC voltage having been induced at the armature winding 16a is converted to a DC power, and the battery 5 is charged.
Now, an example of a construction of a conventional power module for use in the mentioned power element unit 4 is shown in FIG. 14. The power element 41a forming the upper arm 46 and the power element 41b forming the lower arm 47 are connected to a metal substrate 20, and further connected to a heat sink 22 via a radiation grease 21. The connection part between the two power elements 41a and 41b is connected to an AC wiring 9, so that they include different potentials respectively, thus being insulated on an insulating substrate 23. Heat of the power elements 41a and 41b is transferred to the heat sink 22 via the insulating substrate 23, and is radiated in air. An electric heat path of the power elements is formed of a chip 24, being a heating element, a heat spreader 25 acting as a connection element to the outside, and a solder 26 providing connection therebetween. Respective heat conductivities are 0.0254 W/m·K, 0.0293 W/m·K, and 0.0165 W/m·K.
On the other hand, a heat conductivity of the insulating substrate 23 is 0.07 to 0.09 W/m·K. Since an insulator is interposed in heat transfer path, heat dissipation is largely impaired.
As described above, to dispose an inverter in the vicinity of an electric rotating machine, it is essential to ensure heat dissipation of a power element. Nevertheless, an electric rotating machine generates heat, so that temperature environments therearound are tough. Further, due to that a control device containing power elements, being heating elements, is located in the vicinity of the electric rotating machine, temperatures further rise, resulting in a problem of destruction of the power element or control element.